The present application relates to a liquid crystal molecule, and to a liquid crystal display device and a liquid crystal optical spatial modulation device which use the liquid crystal molecule.
In recent years, liquid crystal display devices (LCD) of the active matrix drive type such as TFTs (Thin Film Transistors) have come to be used widely, in the range from small mobile use to large TV sets. In addition, the LCDs have been being enhanced in response speed by adopting new techniques such as impulse drive. Notwithstanding this trend, however, the LCDs are still inferior to plasma displays (PDP), field emission displays (FED) and the like in display quality regarding dynamic images due, for example, to dynamic image blur arising from the slow response speed of the liquid crystal material itself.
Meanwhile, attempts have been being made to enhance the speed from the current 60 Hz frame rate drive to 120 Hz or 240 Hz (high frame rate drive) and to enhance the dynamic image display quality. The dynamic display quality in the LCD depends mostly on the response characteristics of the liquid crystal material itself, though depending partly on the drive system including TFTs. In other words, the above-mentioned problem may not radically be solved, and the high frame rate drive may not be realized, unless the liquid crystal material comes to be capable of high-speed response.
Thus, there is a keen demand for a liquid crystal material which can cope with the high frame rate drive and which can exhibit high-speed response permitting the realization of a high dynamic image display quality.
Examples of the liquid crystal known to be able to realize high-speed response include the nematic liquid crystal attended by the flexoelectric effect, the ferroelectric liquid crystal, and the antiferroelectric liquid crystal. The present inventor has paid attention to the electroclinic effect in the smectic A phase.
The electroclinic effect is the phenomenon in which when an electric field is impressed on liquid crystal molecules uniaxially aligned in the smectic A phase, the optical axis of the liquid crystal molecules (the liquid crystal molecule longitudinal axis) is inclined according to the intensity of the electric field (refer to Garoff, et al, Physical Review Letters, Vol. 38, 1977, p. 848, hereinafter referred to as Non-Patent Document 1). When this type of cell is disposed between orthogonal polarizing plates, a transmitted light quantity according to the angle (tilt angle) between the optical axis of the polarizing plate and the optical axis of the liquid crystal is obtained (formula (A)), and a maximum transmittance is obtained at a tilt angle of ±45°.T/T0=sin2(2θ)×sin2(πΔnd/λ)   (A)
where T is transmitted light quantity, T0 is incident light quantity, θ is the angle (tilt angle) between the optical axis of the polarizing plate and the optical axis of the liquid crystal, Δn is the birefringence of the liquid crystal, d is the thickness of the liquid crystal layer, and λ is the wavelength of the transmitted light.
The dependency of the transmittance on the tilt angle, in the case of a retardation (=Δnd) giving the maximum transmittance, was calculated by formula (A), the results being shown in FIG. 8.
The response time in the electroclinic effect is as short (fast) as several to several tens of microseconds. In addition, there is the merit that the optical axis inclination angle (tilt angle) is proportional to the field intensity (i.e., voltage modulation of transmitted light is possible) when the field intensity is low. In other words, this is a display mode very much suited to the active matrix drive.
However, the tilt angles in the electroclinic effect developed hitherto with liquid crystal materials have not been so large, and sufficient optical modulation has not been obtained successfully.
Examples of a liquid crystal material which shows a large tilt angle include materials in which a siloxane is added to a non-chiral terminal end. The reason for the large tile angle is considered to lie in that the addition of the siloxane, which is a functional group being larger in volume than ordinary alkyl chains and being flexible, to the terminal group of a molecule renders a core portion of the molecule (which portion contributes to optical modulation) more easily movable under the action of an electric field. According to Naciri, et al. Chem. Mater. 1995, 7, pp. 1397-1402, hereinafter referred to as Non-Patent Document 2, in the cases of liquid crystal molecules with a structure in which a siloxane is added to a non-chiral terminal end, a maximum tilt angle of 26° has been obtained. However, it is seen from formula (A) that the transmittance obtainable with the tilt angle of 26° is about 60% at best, which is still insufficient in consideration of putting a display device or the like including the liquid crystal material into practical use.